Competition and productivity in associations of beans (phaseolus vulgaris L.) and beets (beta vulgaris L.) grown at two levels of soil fertility

Plant competition for resources is a major component of plant interference. Field experiments were conducted in the summers of 1994 and 1995 to study competition at two soil fertility levels. Mixtures and pure stands of beans (Phaseolus vulgaris L.) and beets (Beta vulgaris L.) were established, involving nine population density combinations and three pure stand densities per species. Density treatments were assigned to sub-plots, with two soil fertility levels as the main plots in a split plot randomized complete block design. Treatment effects were evaluated using several analytical procedures. Analysis of variance showed that mean yield per plant significantly responded to population density of each species. Interactions between species, and species and fertilizer, were occasionally significant. Inverse yielddensity regressions indicated that beans were the stronger competitor in 1994, but beets were the stronger competitor in 1995. In both species, competition for soil resources seemed to be more important than competition for light, and competitive responses were stronger in the fertilized treatment. Plant proportions were affected by experimental treatments. In beans, dry matter allocation to pods predominated in 1994, but allocation to stems was larger in 1995. In beets, dry matter allocation was dominated by storage root formation in both years. Allometric analysis detected adjustments in plant allometry, although direct, i. e. nonallometric, experimental influences on dry mass per plant also occurred. Yield component analysis indicated that for both species leaf area index was the most important direct contributor to yield variation, while for beans pod filling was also important. In both years and at the higher soil fertility level, the relative productivity of mixtures per unit land area slightly exceeded that of pure stands, as indicated by relative yield total (RYT) and relative land output (RLO) exceeding 1.0. The combined total productivity of the associations (i. e. total land output, TLO) was strongly influenced by the performance of beets, the more productive of the two species. Relative indices of mixture productivity (RYT or RLO) are poor indicators of total productivity (TLO). Overall, these investigations provide some connections among the competitive responses of the associated species, their growth, and their complementary productive performance.Land and Food Systems, Faculty ofGraduat